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VFORK(2)		       System Calls Manual			VFORK(2)

NAME
     vfork -- create a new process without copying the address space

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <unistd.h>

     pid_t
     vfork(void);

DESCRIPTION
     Since  this function is hard to use correctly from application software, it
     is recommended to use posix_spawn(3) or fork(2) instead.

     The vfork() system call can be used to create new processes  without  fully
     copying  the  address  space  of the old process, which is inefficient in a
     paged environment.  It is useful when the purpose	of  fork(2)  would  have
     been  to  create a new system context for an execve(2).  The vfork() system
     call differs from fork(2) in that the child borrows  the  parent  process's
     address  space  and the calling thread's stack until a call to execve(2) or
     an exit (either by a call to _exit(2) or abnormally).  The  calling  thread
     is  suspended  while  the child is using its resources.  Other threads con-
     tinue to run.

     The vfork() system call returns 0 in the child's context  and  (later)  the
     pid of the child in the parent's context.

     Many  problems can occur when replacing fork(2) with vfork().  For example,
     it does not work to return while running in the child's  context  from  the
     procedure	that called vfork() since the eventual return from vfork() would
     then return to a no longer existent stack frame.	Also,  changing  process
     state  which is partially implemented in user space such as signal handlers
     with libthr(3) will corrupt the parent's state.

     Be careful, also, to call _exit(2) rather than exit(3) if	you  cannot  ex-
     ecve(2),  since  exit(3)  will  flush  and close standard I/O channels, and
     thereby mess up the parent processes standard I/O data  structures.   (Even
     with  fork(2) it is wrong to call exit(3) since buffered data would then be
     flushed twice.)

RETURN VALUES
     Same as for fork(2).

SEE ALSO
     _exit(2), execve(2), fork(2),  rfork(2),  sigaction(2),  wait(2),	exit(3),
     posix_spawn(3)

HISTORY
     The vfork() system call appeared in 3BSD.

BUGS
     To  avoid a possible deadlock situation, processes that are children in the
     middle of a vfork() are never sent SIGTTOU or SIGTTIN signals; rather, out-
     put or ioctl(2) calls are allowed and input attempts result in  an  end-of-
     file indication.

FreeBSD ports 15.quarterly	  May 22, 2016				VFORK(2)

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